Hydraulic braking systems in vehicles

ABSTRACT

A vehicle braking system has two independent sources of pressure fluid, one powered by a mechanical pump the other by an electrical pump. Each wheel brake has two actuators, each actuator connected to a different pressure source. The hydraulic pressure supplied to both actuators of a wheel brake is regulated by means sensitive to the deceleration of the wheel.

United States Patent Spence [4 Nov. 6, 1973 HYDRAULIC BRAKING SYSTEMS IN3,677,607 7/1972 Schultz et a1 188/106 P x VEHICLES 3,672,729 6 1972Blakey 188/106 P x 3,610,702 10/1971 MacDuff 303/10 X [75] Inv nt r: ugy p t 3,067,842 12/1962 Smith 188/345 Warwickshire, England 3,679,0307/1972 Kawabc.... 188/106 P [73] Assignee: girling timing, Tyszl y,FOREIGN PATENTS OR APPLICATIONS l 1,388,448 12 1965 France 303 10 [22]Filed: Jan. 7, 1972 [2]] Appl. No.: 216,211 Primary Examiner-M. HensonWood, .Ir. Assistant Examiner.lohn J. Love Attorney-Imirie & Smiley [30]Foreign Application Priority Data Jan. 15, 1971 Great Britain 2,059/71Mar. 2, 1971 Great Britain 5,831/71 [57] ABSTRACT [52] Us. CL 303/10303/15 188/106 P A vehicle braking system has two independent sources[51] Int. Cl 9 B60t 13/16 of pressure fluid, one powered by a'mechanicalpump [58] Field 01 15 6 the other'by an electrical pump. Each wheelbrake has g 3 two actuators, each actuator connected to a different Ypressure source. The hydraulic pressure supplied to [56] ReferencesCited both actuators of a wheel brake is regulated by means 9 1sensitive to the deceleration of the wheel. UNITED STATES PATENTS3,524,683 8/1970 Stelzer 303/10 X 7 Claim S, 2 Drawing Figures PATENTEDNOV 6 i975 SHEET 10F 2 PATENTEDHUV s 1913 SHEET E OF 2 HYDRAULIC BRAKINGSYSTEMS IN VEHICLES This invention relates to hydraulic braking systemsfor vehicles.

According to our invention an hydraulic braking system for a vehiclecomprises two different sources of hydraulic fluid under pressure, eachsource being connected to the brakes of at least one front wheel and atleast one rear wheel so that the brakes on four wheels of the vehicleare supplied with pressure fluid.

Each pressure source may be connected to the brakes of one pair ofdiagonally opposite wheels. Or each pressure source may be connected tothe brakes of two front wheels and one rear wheel.

Preferably each of the brakes of two front wheels and two rear wheelshas two separate actuators and each of the actuators is connected to adifferent pressure source.

In all these systems, if one pressure .source fails, the brakes on atleast one front and one rear wheel can still be operated.

The pressure sources each comprise a pump, or an hydraulic accumulatorpressurised by a pump, and each pump is driven by an independent energysource. Conveniently one pump is mechanically driven from the primemover of the vehicle and the other pump is electrically driven. 1 v

Thus, when the prime mover is idling there may be insufficient outputfromthe mechanically driven pump to maintain adequate hydraulic pressureto operate a wheel brake. Under such conditions the electrically drivenpump will still function. Conversely if a fault in the electrical systemcauses an inadequate output from the electrically driven pump, themechanically driven pump will still function. It is most unlikely thatboth pumps will fail at the same time.

The supply of hydraulic fluid from each source to the wheel brakes iscontrolled by a single control valve assembly. Means may be incorporatedfor indicating the differential pressure between the two pressuresources, preferably downstream of the control valve assembly.

A braking system, according to our invention, may incorporate means forregulating the hydraulic pressure supplied to an actuator of a wheelbrake when the deceleration of the wheel exceeds a predetermined value.In systems in which a wheel brake has two actuators supplied fromdifferent pressure sources, the hydraulic pressure supplied to bothactuators is regulated.

An embodiment of our invention is illustrated in the accompanyingdrawings in which FIGS. 1 and 2, taken tuator of each brake issufficient to effect efficient op- I eration of that brake.

As illustrated the control valves 7 and 8 are combined into a singleassembly 9 and are operated simultaneously by a pedal 10 coupled to theoperating pistons of the control valves through a balance bar.

together, show an hydraulic braking system for a vehi- The piston of thecontrol valve 7 works in a bore 13 defining a pressure space which isconnected through an-outlet port 14 and pipe-lines to the four hydraulicactuators 5.

Similarly the piston of the control valve 8 works in a bore 15 defininga pressure space which is connected through an outlet port 16 andpipe-lines to the four hy-. draulic actuators 6.

The pressure spaces of the control valves are connected to separate andindependent pressure sources through ports 17 spaced forwardly of theinner. end of the pistons.

As illustrated the pressure source connected to the pressure space 13 ofthe control valve 7 comprises a pump 18 which is driven by the engine ofthe vehicle. The pump 18 draws hydraulic fluid from a reservoir 19through a pipe-line 20 in which is located a filter 21 and pumps it toan hydraulic accumulator 22 through a pipe-line 23 and an unloader valve24. The unloader valve 24 incorporates a one-way valve 25 through whichfluid is pumped to the accumulator 22, and a by'- pass passage 26 isconnected between the upstream side of the one-way valve 25 and a returnpipe-line 27 to the reservoir 19..A one-way valve-28 incorporated in thebypass passage 26 opens to allow fluid to be The unloader valve 24 isprovided with a warning light -29 which is energised when the pressureof fluid in the accumulator is below a predetermined value.

The accumulator 22 is connected to the port 17 in the control valve 7through a pipe-line 30, and the port 17 is normally closed by aspring-loaded tilting valve. A second spring-loaded tilting valve, whichis normally held in an open position by the piston, controlscommunication through a port 33 communicating with the pressure space 13and connected to the reservoir 19 through a return line 34.

The pressure source connected to the pressure space 15 of the controlvalve 8 comprises a pump 35 which is driven from an electric motor 36through a cam or gear box 37. The pump 35 "draws hydraulic fluid from areservoir 38, which is indepen'dent of the reservoir 19, through apipe-line 39 in which is located at filter 40, and fluid is pumped to anhydraulic accumulator 41 through a pipe-line 42.

The accumulator 41 is connected to the port 17 of the control valve 8through a pipe-line 44, and the port 17 is normally closed by aspring-loaded tilting valve. A second spring-loaded tilting valve, whichis'normally held in an open position by the piston, controlscommunication through a port 47 communicating with the pressure space 15and connected to the reservoir 38 through a return line 48.

The accuniulator'4l is supplied via an unloader valve 24 which unloadsto reservoir 38 through pipe-line 43. Both reservoirs 19 and 38 areprovided with fluid level warning lights 31.

When the system is operating normally and both accumulators are fullycharged, operation of the pedal 10 of the control valve assembly 9advances both pistons simultaneously to allow the tilting valves toclose ports 33 and 47. Further movement of the pistons in the samedirection opens the tilting valves controlling ports 17 so'that fluidunder pressure is supplied to the two sets of actuators 5 and 6simultaneously to apply the brakes.

When the vehicle is operating under conditions in which the engine isidling for a period and the foot pedal 10 is de-pressed to operate thebrakes a number of times within that period, the pump 18 will be drivenat a speed which is insufficient to maintain a predetermined workingpressure in the accumulator 22. Thus the accumulator 22 will eventuallybecome exhausted. Under such conditions the brakes are applied by meansof the actuators 6 to which fluid under pressure is supplied from theaccumulator 41.

Should the electric motor 36 or the pump 35 fail, under normal operatingconditions the brakes can be operated effectively by the actuators 5supplied with fluid under pressure from the accumulator 22.

Means 53 are incorporated for indicating the differential pressurebetween the outlet 14 and 16 and the actuators-5 and 6 which theysupply. These means 53 from the subject of a U.S. Pat. application No.33171 /69 and need not be described further herein.

In a modification to the systemdescribed pumps 18 and 35 draw from acommon reservoir and the unloader valves 24 discharge into the samereservoir.

In another modification accumulator 41 is charged directly through aone-way valve, the electric motor 36 being controlled by a switchsensitive to the pressure in pipe-line 42 or accumulator 41.

The braking system illustrated in the drawings incorporates means forregulating the hydraulic pressure supplied to the actuators 5 and 6 whenthe deceleration of a wheel exceeds a predetermined value i.e. thesystem is protected against wheel slip or skid.

In the drawings fluid under pressure from the independent pressuresources is supplied to the actuators 5 and 6 of each wheel brake througha tandem modulator 60. Each tandem modulator is of the kind described inthe Complete Specification of our copending cognate U.S. Pat.application Nos. 531/70, 43814/70 and 43815/70 with reference to FIGS.5, or 8 of the drawings; in the Complete Specification of our co-pendingU.S. Pat. application No. 45705/69 with reference to FIG. 5; or in theComplete Specification of our copending cognate U.S. Pat. applicationsNos. 6467/70, 13117/70 and 43813/70 with reference to FIG. 4 of-thedrawings.

The operation of each tandem modulator 60 is controlled by asolenoid-operated control valve 61. Each solenoid-operated control valve61 may be of the kind described in Complete Specification of copendingPat. application No. 45705/69 with reference to FIG. 3 of theaccompanying drawings; in the Complete Specification of our co-pendingcognate U.S. Pat. applications Nos. 531/70, 43814/70 and 43815/70 withreference to FIG. 3 of the accompanying drawings; and in the CompleteSpecification of our co-pending cognate U.S. Pat. applications Nos.6467/70, 13117/70 and 43813/70 with reference to FIG. 3 of theaccompanying drawings. Preferably, however, each solenoid-operatedcontrol valve 61 is in accordance with the construction described in theComplete Specification of our copending cognate U.S. Pat. applicationsNos. 9769/70 and 131 16/70.

The solenoid-operated control valves 61 of the tandem modulators of thebrakes 1 and 2 on the front wheel of the vehicle are each adapted to beenergised by the D.C. output from an electronic control module 62 whichreceives an A.C. output signal from .an electrically inductive sensor 63sensing the deceleration of that wheel.

Similarly the solenoid-operated control valve 61 of the tandemmodulators of the brakes 3 and 4 on the rear wheels of the vehicle areboth adapted to be energised simultaneously by a D.C. output from commonelectronic control module 64 which receives A.C. output signals fromelectrically inductive sensors 65, each sensing the deceleration of oneof the rear wheels.

The tandem modulators 60 are normally held in open positions, in whichfluid under pressure can be supplied the independent pressure sourcessimultaneously to at least one of the actuators 5 and 6 of each wheelbrake, by pressure fluid supplied to one side of the movable wall ofeach modulator through a pipe-line 66 and the control valve of thatmodulator. A separate supply of pressure fluid is provided for thebrakes on the front wheel of the vehicle, and for the brakes on the rearwheels of the vehicle, (reference numberals are only applied to thesupply of pressure fluid for the front wheel brakes, the supply to therear wheel brakes being the same). Each supply comprises an electricallydriven pump 67 which is energised by an electrical storage battery 68and which is connected to the pipe-line 66 on the downstream side of alow-pressure switch 69. The pump 67 is supplied with fluid from areservoir 70 connected to a return and exhaust line 71 from each of thetwo solenoid-operated control valves 61, and the pump 67 is providedwith an electrical cut-off which switches off the pump at apredetermined delivery pressure, for example 300 psi.

A pressure relief valve 72 is located between the pump 67 and thelow-pressure switch 69. When the pressure 'of fluid supplied by the pump67 exceeds a predetermined pressure, substantially higher than that atwhich the low pressure warning switch 69 is energised and the electricalcut-off for the pump 61 fails, the relief valve 72 places the pump 67and the pipe-line 66 in communication with the reservoir through abypass line 73.

Should the pressure on the discharge side of the pump 67 and in thepipeline 66 drop below the predetermined minimum value, the low pressureswitch 69 energises a relay 74 to make a circuit with the battery 68 andenergise the pump 67.

When the deceleration of a front braked wheel exceeds a predeterminedvalue, the control module 62, in response to a signal from the sensor 63of that wheel, energises the solenoid of the control valve 61 to whichit is connected which, in turn, causes fluid under pressure from thepump 67 to be supplied to the opposite side of the movable wall .of thetandem modulator 60. The supply of fluid under pressure to the oppositeside of the movable wall moves the expander pistons in the.

tandem modulator 60 in a direction to cut-ofi the supply of fluid to theactuator 5 and 6 of that brake from the independent pressure sources.Thereafter, further movement of the expander pistons in the samedirection relieves the pressure of fluid applied to the actuators 5 and6 by increasing the effective volumes of the chambers in the modulatorthrough which fluid is supplied to the actuators 5 and 6.

When the deceleration of that wheel is reduced to a value equal to orbelow the predetermined value, the control module de-energises thesolenoid of the control valve 61 and the expander pistons move in theopposite and cut-off and subsequently relieve the braking pressureapplied to the actuators 5 and 6 of both rear wheel being controlled byhydraulic fluid under pressure.

2..A braking system as in claim 1 in which each of the first and secondpumps is connected to the brakes of one pair of diagonally oppositewheels.

3. A braking system as in claim 2 in which each of the first and secondpumps is connected to the brakes of 1 two front wheels and one rearwheel.

brakes from the independent pressure sources as described above inconnection with the cut-off and relief of the braking pressure appliedto a front wheel brake.

I claim: 7

1. An hydraulic braking system for a vehicle having a prime mover and atleast front and rear wheels, comprising a hydraulically operated brakefor each vehicle wheel, a first pump mechanically driven by the primemover of the vehicle,- a second electrically driven pump, means fromeach pump supplying hydraulic fluid under pressure to the wheel brakesof at least one front wheel and at least'one rear wheel of the vehicleso that the brakes on four wheels of the vehicle are supplied withpressure fluid, and means for modulating the pressure of fluid suppliedto the brakes under skid conditions and comprising a modulator having avariable volume chamber connected in the supply of pressure fluid to awheel brake, the volume of the chamber 4. A' braking system as in claim1 in which each wheel brake has two separate actuators, one connected tothe first pump and the other connected to the second pump, and a singlecontrol valve assembly controls the supply of hydraulic fluid from thefirst and second pumps to the wheel brakes.

5. A braking system as in claim 4 in which the control valve assemblycomprises two' pistons operated simultaneously by the same pedal, eachpiston, when operated opening a tipping valve controlling a port in thevalve assembly connected to one of the first and second pumps.

6. A braking system as. in claim 4 wherein said modulating meanscomprises a third pump controlling the volume of said chamber.

7. A braking system as in claim 6 in which a tandem modulator having twovariable volume chambers modulates the pressure of fluid supplied toboth actuators of each wheel brake, and two third pumps are provided,one for the modulators on the front wheels and

1. An hydraulic braking system for a vehicle having a prime mover and at least front and rear wheels, comprising a hydraulically operated brake for each vehicle wheel, a first pump mechanically driven by the prime mover of the vehicle, a second electrically driven pump, means from each pump supplying hydraulic fluid under pressure to the wheel brakes of at least one front wheel and at least one rear wheel of the vehicle so that the brakes on four wheels of the vehicle are supplied with pressure fluid, and means for modulating the pressure of fluid supplied to the brakes under skid conditions and comprising a modulator having a variAble volume chamber connected in the supply of pressure fluid to a wheel brake, the volume of the chamber being controlled by hydraulic fluid under pressure.
 2. A braking system as in claim 1 in which each of the first and second pumps is connected to the brakes of one pair of diagonally opposite wheels.
 3. A braking system as in claim 2 in which each of the first and second pumps is connected to the brakes of two front wheels and one rear wheel.
 4. A braking system as in claim 1 in which each wheel brake has two separate actuators, one connected to the first pump and the other connected to the second pump, and a single control valve assembly controls the supply of hydraulic fluid from the first and second pumps to the wheel brakes.
 5. A braking system as in claim 4 in which the control valve assembly comprises two pistons operated simultaneously by the same pedal, each piston, when operated opening a tipping valve controlling a port in the valve assembly connected to one of the first and second pumps.
 6. A braking system as in claim 4 wherein said modulating means comprises a third pump controlling the volume of said chamber.
 7. A braking system as in claim 6 in which a tandem modulator having two variable volume chambers modulates the pressure of fluid supplied to both actuators of each wheel brake, and two third pumps are provided, one for the modulators on the front wheels and the other for the modulators on the rear wheels. 